Alternatively, if you're not familiar with structs you could use a different approach.
You'll need to code you're own sort, and when you do the comparison you'll need to swap all four of the array elements.

Use typedef to keep your code neater, as you can now just use NAMEOFTYPEDEF struct_name; to create this struct in memory. To access individual data members, use struct_name.a, struct_name.b, etc. If you are using a pointer, eg:

NAMEOFTYPEDEF *struct_ptr = malloc(sizeof(NAMEOFTYPEDEF));

You can access each member by using the -> operator (for example, struct_name->a).

Edit: Additionally, I noticed that this was posted in the C++ board. You can use a class instead of a struct, if you so choose. A class may have members that are functions (also known as methods), whereas a struct may only contain data (you can emulate methods inside of structs using function pointers, but a function pointer is still considered data).